Electrical wave transforming system



Dec. 22, 1953 M. E. MOHR 2,663,795

ELECTRICAL WAVE TRANSFORMING SYSTEM Filed Aug. 19, 1941 3 Sheets-Sheet l FIL LE 0 INPUT Q, VOLTA as i //v VENTOR M E. MOHR A TTORNEV Dec. 22, 1953 M. E. MQHR 2,663,795

ELECTRICAL WAVE TRANSFORMING SYSTEM Filed Aug. 19, 1941 5 Sheets-Sheet 2 FIG. 2 0

F/G.3 a

FIG] 3 v WE F/GJZ 3 & mg M2 5 INPUT F/GJ3 A B VOLTAGE FIG/4 AVOLTAGE DROP IN TUBE PLUS CA 771005 RESISTOR VOLTAGE 29 0 w GROUND Q VOL774GE DROP uv was PLUS umons RESISTOR FIG. /5

-- GROOUND FIG.) Fla/0 FIG. 0 GON- CON- CONDITION ATTORNEV Dec. 22, 1953 M. E. MOHR 2,653,795

ELECTRICAL WAVE TRANSFORMING SYSTEM Filed Aug. 19, 1941 5 Sheets-Sheet a FIG/8 69 5 GAS-FILLED 30 clgg fr 70 50 ASIN FIG.I

r [/0 INPUT 76 I '1 '1 W I I 531114;- LLLLLLL I21 FIG/9 11 I VOLTAGE GROUND voLrs m BATTERY 75 6) vol. TA 05 Y e y m anouuo A TTORNEY Patented Dec. 22, 1953 UNITED" STAT ES;

PATENT OFFICE ELECTRICAL-WAVE TRANSFORMING SYSTEM Milton eE. Mohr, Jamaica, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N..Y.', aicorporation ofNew York Applioation-Allgustli), 1941} Serial N0."407;461-

9 -Claims...

The present inventionirelates to electricalwave: translation; to change-a gradually varying: am-.-- plitude wave into a' wave whoseamplitude-wis varied abruptly in steps.

An object of'the invention is toefiect thistype oi'wave translation with accuracyand without substantial time-delay.

In the specificembodimentof theinvention to be disclosed in this application, triggerr'tubes,

such as gas-filled tubes; areu'sedi'tor'connect into the circuit resistances in different combinations, these resistances operating-similarly tora'potentic-meter to apply to the output terminals different voltages in" steps in response to rising ior" falling.

voltage at the input.-

This specific disclosure represents the" best? form that the present applicant has thus far devised for accomplishingthis object but-it isreale iaed that the circuit maybe widelyvaried by sub--- stitution of equivalent or nearlyequivalent 'means at various points and no attempt ismade'to'il lustrate such alternative constructions. claims to be foundat the end of'this specification are not to be construedas limited to the particular form or forms disclosed.

The nature of the invention and itsvarious features and objects will appear more fullyasthe description proceeds.

In the attached drawings, forming a part of this specification,

Fig. 1 is aschematic' diag-ramof one over-all circuit for accomplishing-the object of'the in vention;

Figs. 2

of thecircuit of Fig. 1

Figs. 9, l and 11 are simplified impedance or voltage diagrams illustratingdifferent circuit conditionsforthe system of Fig-I 1-;

Fig. 18 is a-schematic'diagram of a system using'an alternative type of energizing-voltage for a voltage-dividingcircuit of the type shown in Fig: 1; and

Fig; 19 shows graphs'to' be referred" to -in-the description or" the operation 'of thecircuit -oi Fig. 18: 7

While the invention is of general application;

one use to which it may be putis the subdivisiom of. gradually varying voltage or current-' waves into'stepped waves in' 'certain' systems ior' a-n'alyz ing or synthesizing speech-waves: 0ne*such sys'- tem is disclosed 'iilfilfl article "entitled Thezcar: rier-nature of speech b'yi-Imer Dudley; pub lished-in iiell's'yste n Technical Journalfor-Octoa ber lQ ifl} volume" 19; pages 945316 5151, Fig g' The:

to 8 and l2" to- 17" show graphs-toebe referred to in the description of the operation' of that publication shows an oscillogram. of'

speech-defining signals .of low frequency (0 150 cycles) obtained by analysis. of spoken words. 1

These. speech defining currents exhibit grado ually-rising-and falling amplitude and-the. in! vention may be used to translate such currents int-o currents having generally similar wave form. but rising and falling'in aseries of abruptsteps instead of by smooth gradations The voltage. in

signals through resistancesmay be steppedup,

if necessary by vacuum tube amplifiersto the proper levels to fit the characteristicsct the trigger tubes employed in the embodiment of *theinvention disclosed herein. 7

Referring to-Fig. 1, the input vol-tage-isapw plied to the terminals i0 andthe output voltage of'st'epped characteristic may be taken oii at terminals I! or a-t-terminals iii. A plurality of in a manner to be described,- between-the input.

and output terminals. Opposing voltage sources l6=and 11 0f graduated-value are inserted between the ungrounded input terminal 1 3 and the- 2 grid of the respective tubes [2, i3. Bias-voltages 18* and 19,- all having the same-vane; are connected-to the-grids -of the tubes iii-andl5. Thecathodesoitubes l2; Hi, are connected together and through a-resistance 20 and-inductinductance is-shown at 22, 23 for the cathodes nested through-an: individual resistance Zit -to a leadi2lleadingto the anode of the pentod'e 4G: Theanodesof the left-hand tubes l3, I2 are' connected through individual resistances M and:

it'to the ungrounded outputterminal-l I. In oneembodiment the resistances 29" had a value of 30,000 ohms; resistances Ziiand 22 each had*a=- 40-" value of 10.000 ohms and the resistancesz i *and" 25 each had a value of 250,000 ohms, these'valizes being by way ofexample' and 'noticriti'cal.

At'theupper portion of'the figure" there is shown an iinpulsing circuit for controllingthe s operation of the gas-filled'tubes i2; i3, i i' 'an'd" developed by the flow of these. speech defining gas-filled tubes 12,- !3; is and ib are connected.

ance 2| to ground; A similar'resistance and? ground. Battery 38 having its center point grounded is connected to the diodes in such polarity as to oppose the current flow in re sponse to driving voltages developed in windings 3i and 32.

lhe operation of this part of the circuit for producing controlling pulses is indicated by certain of the curves given in 2 to S. The sine wave curves in Figs. 2 and 3 show the voltages applied to the clipper circuit. The voltage of Fig. 3 is displaced in phase with respect to that in Fig. 2 by means of the phasing elements 33, The action of the diodes in limiting the amplitude of the wave applied to the output resistor as is shown by the dotted horizontal lines. indi cating that most of the voltage wave is suppressed. Figs. t and 5 show with an enlarged ordinate scale the shape of the current wave transmitted to the output resistor 1:": from the respective pairs of diodes.

The resistance ib is center-tapped and is cou pled through a rectifier diode ti and resistances 52 and ts to the grid of the pentode M. The result of the addition of the voltages given in the curves of Figs. 4 and 5 in the resistance 49 is shown by the short positive and negative pulses of Fig. 6. Only the positive pulses, shown in Fig. 7, are transmitted through the rectifier 4!. The resulting voltage wave in the output of pentode 6.4 is indicated in Fig. 8 comprising a constant portion with very abrupt depressions resulting from the amplification of the impulses of the type shown in Fig. '7.

The operation of the gas-filled tubes and their associated resistances in producing a stepped output voltage will now be described with the aid of the simplified diagrams of Figs. 9, l and 11 and the graphs given in Figs. 12 to 1'7. It will be assumed that a gradually varying input voltage such as indicated in Fig. 13 is applied to terminals I8. Fig. 12 shows the character of the voltage wave that is applied to the gas-filled tubes from conductor 2?. The curves in these figures are somewhat idealized but serve to illustrate the principles of operation.

If the voltage wave at terminals IE} is too small to produce the smallest voltage that is desired across the output terminals N, that is, an input voltage less than the value A in 13, such input wave fails to overcome the opposing voltage I6 (which is smaller than i 'l) and. fails to initiate discharge in tube it when the anode of the latter is driven positive by the voltage applied over lead 27. Voltages impressed on the grids of the tubes is and I from the batteries is and it are such as to permit the tubes it and E5 to become ionized and the interconnections between the tubes of each pair are such that only one tube of a pair can be ionized at the same time. Tubes It and 15 will become ionized in the event that the opposite tube of the pair is not previously ionized. Under the conditions assumed, therefore, when lead 27 applies positive voltage to the anodes of tubes as and 95, both of these tubes are ionized and the resulting circuit condition corresponds to that shown in diagram in Fig. 9. It is seen from this diagram that the resistances 24 and 25 are connected, in series with individual resistances E9, to lead 2'! so that in the absence of current flow through these resistances the voltage at Q and at R and at P is equal to the positive voltage existing in lead 2'! as indicated in Figs. 14 and 15 in time period T1. It is assumed in the present disclosure that the voltage of battery 26 is just sufficient to redu e n? l r '4 minal voltage II to zero under these conditions. This is indicated at H, Fig. 1'7.

The brief interruption of the voltage in lead 27 at the end of the time interval T1 deionizes the tubes is and i5 and immediately thereafter the full voltage of lead 27 is reapplied to the plates of all of the gas-filled tubes. This brief interruption causes a momentary voltage to be applied to terminals I I from the battery 25 as indicated at J. This is of such short duration that it may readily be suppressed by a low-pass filter, if desired.

It will next be assumed that the input voltage impressed at terminals l 6 is in excess of the value A (Fig. 18) but less than value 3. In the present case the input voltage is sufficient to overcome the opposing voltage It in the input circuit of tube I2 and that tube ionizes before tube It has ionized. The resulting current fiow through resistance 2i! and inductance 2! to ground causes a counter-electromotive force to be developed, raising the potential of both cathodes of tubes l 2 and I4 to such voltage that the anode-cathode voltage appearing across tube is is insufiioient to permit that tube to ionize with the grid bias applied from I8. Tube I5, however, icnizes as in the previous case, since the input voltage is assumed less than value B and tube I3 is not, therefore, ionized.

The diagram representing this circuit condition is given in Fig. 10. It is noted from Fig. 10 that the potential of the point P is approximately the potential of the mid-point of the resistance 29 that is in series with the plate of tube i 5. This is true because the high resistances 25 and 2 2 produce at the point P a potential which is midway between the potentials at Q and R, that is, the potential of the plate of tube I2 and the approximate potential of the conductor 2?, resistances 24 and 25 being, as stated, very large compared with resistances 29. This potential P is indicated in Fig. 16 in the time interval T2. The voltage of battery 26 when subtracted from this potential gives the value K in Fig. 1'7. At the end of the period T2 the interruption of the voltage applied over conductor 27 again deionizes the gas-filled tubes.

Let it next be assumed that the input voltage has risen to a value greater than that indicated at B, Fig. 13. This is sufficient to overcome the opposing bias voltages of both sources It and H in the input circuits of tubes l2 and I3. Both of these tubes, therefore, ionize and prevent ionization of tubes Hi and I5 because of the potential developed across the cathode lead impedances 20, 2! and 22, 23.

The diagram corresponding to this condition is shown in Fig. 11. The potential dividing resistors 24 and 25 are both connected to the anodes of tubes I2 and I3 so that the points Q, R and P now are at the same voltage, corresponding to the voltage of conductor 27 minus the potential drop through either resistance 29 associated with tube I2 or I3. This corresponds to the lowest voltage indicated in Fig. 16. When the voltage of the battery 26 is subtracted from this voltage the voltage L, Fig. 1'7, is obtained which is the voltage applied to the terminals I i.

In effecting the look-out between the two tubes of a pair as mentioned above, the inductance H or 23 develops an initial or transient lock-out voltage and the resistance 2% or 22 provides lockout during the remainder of the cycle. The time constant of the circuit depends upon the relative proportioning of the reactance and resistance and may im tie-practical lea-see beeas esmalltyasia ,iews microseconds: i Lock -out tiss-used-Ftoaassureetliat: once a set of output conditione -is :established Eats the-Joeginningmt l-"a-cycle these- -conditions will; not i: changeuntil the platevoltage in lead 2l haszbeen 6 reduced and *reapplied ir respective -i What-'hap I pens -to-- the;gridwoltage-during: theecycle;

If the in-putsvoltage remains abovathe Val-118 B? Fige 13: for -the duration-of several voltage ime pulses in lead 21, the gas-filled tubes are deionized 10 momentarily-attire end "of each such impulsebut the persistence =of the-input voltage; causes the 1 tubes-"I 2'=and-- I 3 to'be -ionized again and maintain" the voltage conditions as represented-inthetime period-'Ta; Fig? 171 Fordescendinggvaluesnf'the input *voltageavave Fig: .13 the same-action takes place as "fort rising? voltages;- That --is,'- as longas the'in-put -voltage remains above'the *value-B' tubes I 2"-and I3 '--areionized "during eachimpu-lse time; Fig 12; when the-voltage drops to a value-between B and A tubes I 2 "and I Fare-ionized during each impulsetime-andwhen the voltage drops'b'elow the-value Y A tubes I 4-and- I 5 areionizedthroughout eachinm puise-timer Fig: 1 indicates "dotted connectionswhich may" lead to' stilIfurt-herpairs. of gas filledtubes-corresponding to' I3, I5 "and'-'I2;- I4:- For'each-such" additional pair of gas-filled tubes there is'an additional resistance" corresponding told; 25. Threepairs of tubes will .give an output-voltage wave having three stepped values: in" addition to' zero, four pairs-of tubes willigiveiour steps; etc; For :example; referring; to Fig: '.'in' which: as 1 explained, the potential fdividing resistors 24 and" 25i'giye a potential at point P corresponding sub= stantially to the midpptential existing in resistor 29 associatedjwith tube I 5, if an additional "tube 1 liked2f'were'alsoionized atthis time, correspond= I ing to. an input'voltage. intermediate between, A andgB; the. potential of the point tPfwould corre spondfapproximately to appint in resistance ,29; associated; with. tube I 5". onethird .the distance along that resistance, measured from the plate of f tube. I5.. The reason. for. this is that there Would thenbe three potential"dividing resistors, and the potential produced at point P *would be. the same as if the third jresistorwere in. parallel with 25.. Similarly, with four .pairsofi'tubfes =the..po-. tenti'al; existing across one. of; the resistors. 2915 wouldbe effectively. diilidedinto one, two,. threeor foursparts depending uponi .the...par.ticular tubesionizedg'iniany. givencase ..to..provide..for .saztotal i of ifour steps. of values besides the. zero. .value.,

The voltage'iproducedjat terminals ..I l I willlbe stepped asindicatedbythe .wave form shownad-i jacent these term-inalsin. Fig.1 .1 and its phasewill. be opposite .tothat .oi the inputwave because of theaction ofthecircuit' as above...described.l For. somepurposesthe wave .as it appearsat terminals-. may, be suitable: ILQhowever, .it.,isi.desired, to. turnv over .the phase .oithisivoltagenwavaiswitch.l BI is. closed on. contact...62;.anditerminals. I I I are... used as. the... output terminals. Inrth'iseivay. the triodel .60 .islused to. .gi ve the .phase reversah,

The. design lot this vacuum tube istagevmaybe. varied ,to. suit conditions Itlis illustrated. as, a; direct currents-circuit, with... their grids-suitably. biasedjromrbattery v 26,, Plate. voltage issupplied throughresiston 63;,whichmay ,alsonbe. inductive" The normal.voltagethat would be applied to ter..

minals IILir'om across.couplingresistor whom. the applied input voltage is zero maybe canceled; by the counter-potential taken fromypote'ntiometer resistance -61 across a small battery 68'."

1; required: degree of approximation.

Whemthervoltage:atterminalsa! I i hasithe values H-i Eigrl7);-thezslider;on-resistance E! isiadjusted; to give zero voltage-iat'itermina'ls III: WIIerrthervoltage at terminals I I has some. other .value. such assKw'orzL, the grid'of tube Bil ismade more negative-s. this; amount; increasing the internall resistance of the tube filliiwhich makes the potentialriatrpoint-zjfidlmore positive,and therefore they potentiahof theupper/terminal-J I I more positive;

Fig-5r: 182 shows ant-embodiment in which square wavesraresappliemtoctheigasefilled tubes instead of mvavesewith only" very short interruption times asepreviously described. These square waves are produced from sinerwavesegenerated at 36 and transmittedzthroughtransformer 69 to a, clipper.

circuitixonsistingpf:diodes'.'3Ii;.35, 31 and 38st0" theicontrolvgridsofzitwozpentodesE2 and 53. Thed-iodesit 5;; etcag: areself ebiased, by cathode resistors. EBLeachpprovidedavitlisthe usual shunting capacity' fili'. These .adiodes cause flat topped waves-to b'e-xapp'liecl to the grids-0f pentodes 52 and 53.. The-.pentodesare-self+biased by cathode resistor 5' 1 'ishunted-iby'w capacity :55: Output transformer 56s.:is1designed: to :pass square top waves to the The Waves applied to conductor- I2? have the general form shown 'in Fig. 19, lfaphl, consisting of both positiveeand negativeportions.

One-advantageoi using-.wavesof this form is that transformers may -be used for distributing such-waves to-points atwhich they are to be used and they maybe transmitted at any suitable voltage and :transformed at the place where they are used:

Thegapparatus-in the box- Iii may comprise the gas-filled tubes I 2,1. It I 4 I 5 and associated re sistances; inductances I and grid biasing batteries asxshownin-sFigi 1. The-input terminals are in thisecaseiindicatedt.at III); Thepotential divid-- ing; resistances;U anda 25. connect through. a source-10f:opposingzvoltage I 26 and series resistor I I ito.:thegl:id ;of a; .ph'ase reversing amplifier 12.

The operation of this. type of embodiment will be;described.-in connection with the graphs given OlflrFigglQ. Assumingan-input'voltage at lie-of the:generatiorinshown in graph II, 19, it is noted'ithat the. -fi-rst;.positive impulse and the beginningofzthei-second positive impulse (counting fromatheleft). occur beforathe input voltage rises ab0venthe-;va1ue:A.-. This corresponds to the circuitcondition indicated in Fig. 9 so that the voltagemat-W, (Fig e18) is asshown in Fig. 19, graph IIIzatthe corresppnding times.

At thexstartiotthethirdpositive impulse of the wave migraphi the input voltage is intermediate between values-A-and. B. I This corresponds to the circuit:conditionotFig, 10 and gives an inter-- mediatevalueioi voltage-at W as shown in graph IIIfthG third impulse. x

Theofourth:positive-impulse, Fig.v 19, graph 1, oceursrata -;timey;when .the input voltage exceeds the value B. This .coiresponds-tc the circuit conditionfiofi-Fig 11 a-nd1gives. -a minimum value of voltage at tWt- 'ifhisiwa'te inrgraph .111 :is; reversed in phase by thertube 'IZfiQthatathe voltage appearing from :1: groundiszasindicated-ingraph IV. Some of theoriginaliavoltagesfrom. lead. I2? is. taken around throughebiasing:batterygsl fi andiresistor late the ungrounded ou-tput -terminal and is combined with -the output-wavc= in tube; 7 2 arriving 4 at this same pointthrough-*resistor-T5; The voltage taken'irom' lead -I 21 and displaced in the negative direction bythevoltage of battery I5 is indicatewbygraph'v. The-result of algebraic- 7? addition of the voltages represented in graphs IV and V is shown in raph VI, this being the voltage appearing across the output terminals 11.

What is claimed is:

1. In combination, circuit means for converting gradually varying voltage into a voltage varying abruptly in steps comprisin a plurality of trigger tubes, a source of interrupted output voltage of constant peak value for the tubes,

graduated voltage sources connected to the input terminals of said tubes opposite in sign to said gradually varying voltage, means to apply the gradually varying voltage to the input terminals of said tubes in common whereby certain of the tubes are triggered at a time depending upon the instantaneous value of the applied input voltage, output terminals between which said stepped voltage is to be produce, resistances connected in parallel between one of said output terminals and said source, said trigger tubes having output terminals connected to points in the individual resistances and means including the tubes that are triggered at any one time for individually producing a potential drop in the corresponding resistance between said source of interrupted voltage and said output terminals.

2. In combination, circuit means for converting a gradually varying voltage into a stepped voltage comprising trigger tubes in interlocking circuit relation in pairs, graduated voltage sources connected severally to the first tube of each pair,

' means to apply the gradually varying voltage to said first tube of each pair in opposition to said graduated voltage sources to trigger on certain of said tubes depending upon the instantaneous voltage of said applied wave, output terminals, a source of output voltage supply for said tubes, and means including resistances connected between output electrodes of said tubes and said output terminals for producing abruptly changing voltages at said output terminals in response to the triggering on of said tubes under control of the gradual variations in said applied voltage.

3. In a circuit for translating a gradually changing input voltage to an abruptly changing output voltage, a plurality of trigger tubes having graduated triggering characteristics whereby they are triggered selectively by input voltages of different value, means to apply said input voltage to said tubes in common to cause certain of them to be triggered at a time depending upon the input voltage applied, a source of output voltage, output terminals, and resistances individual to said tubes connected in parallel from said source of output voltage to said output terminals, said trigger tubes having output circuits effectively includin a small portion only of the corresponding output resistance whereby when said tubes are triggered abrupt reductions in voltage occur between said source of output voltage and said output terminals depending upon the number of tubes triggered at a time.

4. In combination, a plurality of pairs of gasfilled tubes, a pulsing circuit connected to the anodes of all or" said tubes, means for causing one tube of each pair to break down on each positive pulse from said pulsing circuit, a source of gradually varying input voltage connected to the grid of one tube of each pair, graduated negative bias sources connected to said grids for causing said last-mentioned tubes to be ionized selectively according as the input voltage exceeds the bias on one or more of said last-mentioned tubes, interlocking connections between the tubes of each pair for preventing bot-h tubes from ion- 8. izing during any one pulse, output terminals, resistances connected between said pulsing circuit and said output terminals to provide a voltage at said output terminals of a magnitude determined by the potential drop through certain of said resistances, and connections from points on said resistances to said tubes to enable the output terminal voltage to be varied in steps depending upon which tubes of said pairs of tubes are ionized durin each impulse.

5. In combination, a source of voltage, output terminals, a plurality of resistances adapted when effectively connected in different combinations to said source and said terminals to apply different fractional parts of the voltage of saidsource to said terminals, 3. source of incoming waves of gradually varying amplitude, a plurality of trigger tubes having input electrodes connected in common to said source of input waves, means to initiate discharge in diiierent ones of said tubes in response to input wave variations dependent upon the instantaneous amplitude of said waves and means causing said tubes when triggered to increase the potential drop through portions of said resistances between said source of voltage and said output terminals to apply to said terminals abruptly changing voltage in steps in response to rising and falling voltage of said input waves.

6. In combination, a circuit having a pair of input terminals and a pair or output terminals, a source of slowly varying voltage connected to said input terminals, a source of waves or" flat-top wave form connected in circuit with said output terminals, resistances efiectively included between said latter source and output terminals for reducing in steps the voltage applied to said output terminals when current is caused to flow through said resistances, a trigger tube connected to each resistance and adapted when broken down to produce current flow through the corre sponding resistance and means controlled bythe instantaneous input voltage for determining the number of trigger tubes that are broken down at a time.

7. In combination, a circuit having input terminals and output terminals, a source of fiattopped voltage waves connected to said output terminals, a set of trigger tubes connected in shunt relation to said source and to said output terminals through individual resistances and means for initiating discharge through said tubes during positive periods of said voltage waves to control the maximum voltage applied from said source to said output terminals, a second set of trigger tubes connected in shunt relation to said source and said output terminals through individual resistances, means to initiate discharge in a variable number of said second set of tubes by application of voltage of different value to said input terminals, a source of variable voltage connected to said input terminals, means controlled by tubes in said second'set, when energized, to prevent discharge in corresponding tubes of said first set and means controlled by energized tubes of said second set for reducing the voltage applied from said first source to said output terminals, in steps depending upon the number of tubes in the second set that are energized.

8. In combination, a source of voltage, output terminals, and means for applying various fractional amounts of said voltage to said terminals in abrupt steps under control of a gradually vary ing voltage, comprising resistances connected, in parallel with each other, in series between one terminal of said source and one output terminal,

a connection from the opposite terminal of said source to the other output terminal, each resistance consisting of a small portion adjacent said source in series with a large portion adjacent said one output terminal, a trigger tube for each resistance having its discharge terminals connected from a point in the resistance between said portions across to said connection, a control terminal for each trigger tube, means to apply the gradually varying voltage to the control terminals of all of said trigger tubes in common, and graduated bias voltages for said trigger tubes for causing different numbers of said tubes to be triggered at a time depending upon the instantaneous amplitude of said varying voltage.

9. A circuit for converting a gradually varying current wave into a stepped wave, said circuit having input terminals for application of said gradually varying wave and output terminals across which the stepped wave is to be produced, a group of trigger tubes having control electrodes in circuit with said input terminals and having output electrodes including anodes, a source of regularly recurring positive voltage pulses, means to apply said pulses to the anodes of all of said tubes in parallel to render said anodes positive so as to cause current to flow through said tubes under control of the applied input voltage wave,

10 means to apply blocking potential to the input electrodes of said tubes to prevent breakdown except at the beginning of each of said pulses, means to remove said blocking potential between pulses and to place said tubes under control oi said gradually varying wave for an instant at the beginning of each pulse, means to cause a varying number of said tubes to break down depending upon the instantaneous amplitude of said varying wave, means to cause the tubes that thus break down to remain in conducting condition throughout the ensuing pulse period and to maintain the other tubes of the group non-conducting during such pulse period, and parallel connections from the output electrodes of said tubes to said output terminals, including individual resistors in the conductors from the output electrodes of said tubes.

MILTON E. MOI-IR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,672,215 Heising June 5, 1928 2,038,683 Schramm Apr. 28, 1936 2,095,124 Cockrell Oct. 5, 1937 2,226,288 Pieplow Dec. 24, 1940 2,250,819 Wolf July 29, 1941 

